In terms of pure functionality, the IS2535 and IS3035 are quite similar. They both look for the changes in infrared (IR) energy that occur with movement. Both provide pet immunity of up to 80 pounds when the detector is set on the lowest sensitivity setting. Both devices are wired to a panel in the same manner.

However, there are a few differences between these sensors. The IS2535 has a smaller coverage area at 35 feet by 40 feet. The IS3035 has a coverage area of 40 feet by 56 feet. The IS2535 offers four (4) sensitivity settings, while the IS3035 only has high sensitivity and low sensitivity options. With the IS3035 you can only choose between pet immunity for up to 80 pounds, or OFF. But with the IS2535, you can select pet immunity for up to 80 pounds, up to 40 pounds, or OFF.

There are also some other minor differences between these two devices. They have different dimensions, with the IS2535 being the larger sensor. The dimensions for the IS2535 are 4.375"L x 2.25"W x 1.5"D. The slightly more compact IS3035 has dimensions of 3.86"L x 2.24"W x 1.71"D. Though based on these dimensions, the IS3035 is a bit thicker. These motion sensors also have different appearances, which can be seen in the picture above. Also note that the IS2535 has been discontinued, while the IS3035 is still available at the time of this writing (August 2019).

Various specifications for the IS2535 and the IS3035 can be see in the following table: